Regulation of desmocollin transcription in mouse preimplantation embryos

Overview of junctional complexes during mammalian early embryonic development

Cell-cell junctions form strong intercellular connections and mediate communication between blastomeres during preimplantation embryonic development and thus are crucial for cell integrity, polarity, cell fate specification and morphogenesis. Together with cell adhesion molecules and cytoskeletal elements, intercellular junctions orchestrate mechanotransduction, morphokinetics and signaling networks during the development of early embryos. This review focuses on the structure, organization, function and expressional pattern of the cell-cell junction complexes during early embryonic development. Understanding the importance of dynamic junction formation and maturation processes will shed light on the molecular mechanism behind developmental abnormalities of early embryos during the preimplantation period.

Mitochondrial DNA content and developmental competence of blastocysts derived from pre-pubertal heifer oocytes

In the cattle-breeding industry, there is an increasing demand for in vitro embryo production from pre-pubertal heifers. In this study, we evaluated the differences in mitochondrial DNA content, oxidative stress, and developmental competence in blastocysts derived from pre-pubertal and pubertal heifers. We found higher mitochondrial DNA copy numbers in blastocysts produced from pre-pubertal heifers than from pubertal heifers. In the group of pre-pubertal animals, there was a significantly lower number of blastocysts produced in vitro from the same number of collected oocytes, and these blastocysts did not differ from those obtained from pubertal oocytes in terms of their morphological quality. The morphologically appropriate blastocysts derived from pre-pubertal heifers had higher concentrations of reactive oxygen species and glutathione. In blastocysts derived from pre-pubertal heifers, we found alterations in the expression of gene markers for developmental competence, which correlated with higher mitochondrial DNA content, suggesting a lower quality of blastocysts derived from pre-pubertal animals than from pubertal animals. The inadequate redox balance in blastocysts obtained from pre-pubertal females, along with higher mitochondrial DNA copy number, as well as differential gene expression of markers of developmental competence, elucidate the low quality of blastocysts derived from pre-pubertal animals, despite their unaltered morphology.

Effects of recombinant OVGP1 protein on in vitro bovine embryo development

Previously, our group demonstrated that recombinant porcine oviductin (pOVGP1) binds to the zona pellucida (ZP) of in vitro-matured (IVM) porcine oocytes with a positive effect on in vitro fertilization (IVF). The fact that pOVGP1 was detected inside IVM oocytes suggested that this protein had a biological role during embryo development. The aim of this study was to evaluate the effects of pOVGP1 on bovine in vitro embryo development. We applied 10 or 50 µg/ml of pOVGP1 during IVF, embryonic in vitro culture (IVC), or both, to evaluate cleavage and embryo development. Blastocyst quality was assessed by analyzing the expression of important developmental genes and the survival rates after vitrification/warming. pOVGP1 was detected in the ZP, perivitelline space, and plasma membrane of blastocysts. No significant differences (P > 0.05) were found in cleavage or blastocyst yield when 10 or 50 µg/ml of pOVGP1 was used during IVF or IVC. However, when 50 µg/ml pOVGP1 was used during IVF + IVC, the number of blastocysts obtained was half that obtained with the control and 10 µg/ml pOVGP1 groups. The survival rates after vitrification/warming of expanded blastocysts cultured with pOVGP1 showed no significant differences between groups (P > 0.05). The use of pOVGP1 during IVF, IVC, or both, increased the relative abundance of mRNA of DSC2, ATF4, AQP3, and DNMT3A, the marker-genes of embryo quality. In conclusion, the use of pOVGP1 during bovine embryo in vitro culture does not affect embryo developmental rates but produces embryos of better quality in terms of the relative abundance of specific genes.

Survival of vitrified in vitro-produced bovine embryos after a one-step warming in-straw cryoprotectant dilution procedure

Vitrification is an alternative to slow-rate freezing for cryopreserving bovine embryos. However, this technology requires simplification if it is to be used under field conditions. The main objective of this work was to develop a new system for the direct transfer of vitrified embryos to be used under farm conditions. For this, three objectives were set: (1) to compare the effect of vitrification, using the cryologic vitrification method (CVM), and slow-rate freezing on bovine embryo development and quality; (2) to develop a one-step warming procedure for bovine in vitro-produced (IVP) vitrified (by CVM) embryos; and (3) to assess the effects on embryo survival of a new method for the direct transfer of vitrified IVP bovine blastocysts. In vitro-produced blastocysts were initially either vitrified by CVM or subjected to slow freezing to compare embryo survival and quality (experiment 1). No differences were detected between these cryopreservation techniques in terms of the survival and quality variables at 24 hours or in terms of the proteins expressed. However, at 48 hours the vitrified embryos showed higher hatching rates, greater total cell numbers, and lower apoptotic indices (P < 0.05). In experiment 2, CVM-vitrified IVP blastocysts were warmed by the conventional two-step or one-step warming procedure by incubating them at 41 °C in 0.25 M sucrose for 10 minutes, 0.15 M sucrose for 10 minutes, or 0.25 M sucrose for 5 minutes. In addition, embryo transfer (ET) was performed using vitrified embryos warmed by the one-step procedure in 0.25 M sucrose solution for 5 minutes. As a control group, IVP fresh embryos were transferred to recipient females. No differences were observed in embryo survival or total cell number between any of the warming procedures. Moreover, no significant differences for pregnancy at 60 days were found between the ET groups. In experiment 3, expanded IVP blastocysts were then either vitrified using a conventional or a modified fiber plug designed to allow direct ET after in-straw cryoprotectant (CP) dilution. They were warmed using the one-step process (0.25 M sucrose, 5 minutes) in a 0.25 mL French straw. Embryo recovery associated with the modified fibreplug system was less reliable than with the conventional system. However, no differences were seen between the systems in terms of in vitro embryo survival among those finally recovered. Finally, IVP blastocysts were vitrified using conventional fibreplugs to maintain a high embryo recovery rate, and then warmed using the one-step warming in-straw CP dilution procedure, but using an adapter with a wider opening coupled to the French straw and a heated metal chamber to protect and keep the straw at 41 °C (experiment 4). No differences were seen in embryo survival rates between the two groups. The CVM combined with this new one-step warming in-straw CP dilution procedure could be used for direct ET under field conditions.

Cell fate regulation during preimplantation development: a view of adhesion-linked molecular interactions

In the developmental process of the early mammalian embryo, it is crucial to understand how the identical cells in the early embryo later develop different fates. Along with existing models, many recently discovered molecular, cellular and developmental factors play roles in cell position, cell polarity and transcriptional networks in cell fate regulation during preimplantation. A structuring process known as compaction provides the "start signal" for cells to differentiate and orchestrates the developmental cascade. The proper intercellular junctional complexes assembled between blastomeres act as a conducting mechanism governing cellular diversification. Here, we provide an overview of the diversification process during preimplantation development as it relates to intercellular junctional complexes. We also evaluate transcriptional differences between embryonic lineages according to cell- cell adhesion and the contributions of adhesion to lineage commitment. These series of processes indicate that proper cell fate specification in the early mammalian embryo depends on junctional interactions and communication, which play essential roles during early morphogenesis.

In VivoFunction of Desmosomes

Desmosomes are morphologically and biochemically defined cell-cell junctions that are required for maintaining the mechanical integrity of skin and the heart in adult mammals. Furthermore, since mice with null mutations in desmosomal plaque proteins (plakoglobin and desmoplakin) die in utero, it is also evident that desmosomes are indispensable for normal embryonic development. This review focuses on the role of desmosomes in vivo. We will summarize the effects of mutations in desmosomal genes on pre- and post-embryonic development of mouse and man and discuss recent findings relating to the specific role of desmosomal cadherins in skin differentiation and homeostasis.

Desmosome assembly and dynamics

Desmosomes are intercellular junctions that anchor intermediate filaments (IFs) to the plasma membrane, forming a supracellular scaffold that provides mechanical resilience to tissues. This anchoring function is accomplished by specialized members of the cadherin family and associated cytoskeletal linking proteins, which together form a highly organized membrane core flanked by mirror-image cytoplasmic plaques. Due to the biochemical insolubility of desmosomes, the mechanisms that govern assembly of these components into a functional organelle remained elusive. Recently developed molecular reporters and live cell imaging approaches have provided powerful new tools to monitor this finely tuned process in real time. Here we discuss studies that are beginning to decipher the machinery and regulation governing desmosome assembly and homeostasis in situ and how these mechanisms are affected during disease pathogenesis.

Desmosomal adhesiveness is developmentally regulated in the mouse embryo and modulated during trophectoderm migration

During embryonic development tissues remain malleable to participate in morphogenetic movements but on completion of morphogenesis they must acquire the toughness essential for independent adult life. Desmosomes are cell-cell junctions that maintain tissue integrity especially where resistance to mechanical stress is required. Desmosomes in adult tissues are termed hyper-adhesive because they adhere strongly and are experimentally resistant to extracellular calcium chelation. Wounding results in weakening of desmosomal adhesion to a calcium-dependent state, presumably to facilitate cell migration and wound closure. Since desmosomes appear early in mouse tissue development we hypothesised that initial weak adhesion would be followed by acquisition of hyper-adhesion, the opposite of what happens on wounding. We show that epidermal desmosomes are calcium-dependent until embryonic day 12 (E12) and become hyper-adhesive by E14. Similarly, trophectodermal desmosomes change from calcium-dependence to hyper-adhesiveness as blastocyst development proceeds from E3 to E4.5. In both, development of hyper-adhesion is accompanied by the appearance of a midline between the plasma membranes supporting previous evidence that hyper-adhesiveness depends on the organised arrangement of desmosomal cadherins. By contrast, adherens junctions remain calcium-dependent throughout but tight junctions become calcium-independent as desmosomes mature. Using protein kinase C (PKC) activation and PKCα-/- mice, we provide evidence suggesting that conventional PKC isoforms are involved in developmental progression to hyper-adhesiveness. We demonstrate that modulation of desmosomal adhesion by PKC can regulate migration of trophectoderm. It appears that tissue stabilisation is one of several roles played by desmosomes in animal development.

Preimplantation development regulatory pathway construction through a text-mining approach

Background

The integration of sequencing and gene interaction data and subsequent generation of pathways and networks contained in databases such as KEGG Pathway is essential for the comprehension of complex biological processes. We noticed the absence of a chart or pathway describing the well-studied preimplantation development stages; furthermore, not all genes involved in the process have entries in KEGG Orthology, important information for knowledge application with relation to other organisms.

Results

In this work we sought to develop the regulatory pathway for the preimplantation development stage using text-mining tools such as Medline Ranker and PESCADOR to reveal biointeractions among the genes involved in this process. The genes present in the resulting pathway were also used as seeds for software developed by our group called SeedServer to create clusters of homologous genes. These homologues allowed the determination of the last common ancestor for each gene and revealed that the preimplantation development pathway consists of a conserved ancient core of genes with the addition of modern elements.

Conclusions

The generation of regulatory pathways through text-mining tools allows the integration of data generated by several studies for a more complete visualization of complex biological processes. Using the genes in this pathway as “seeds” for the generation of clusters of homologues, the pathway can be visualized for other organisms. The clustering of homologous genes together with determination of the ancestry leads to a better understanding of the evolution of such process.

Ochratoxin A-induced renal cortex fibrosis and epithelial-to-mesenchymal transition: molecular mechanisms of ochratoxin A-injury and potential effects of red wine

We characterized the effect of chronic ochratoxin A (OTA) on rat kidney cortex, analyzing collagen content and collagen turnover and the major markers of epithelial-to-mesenchymal transition (EMT), such as alpha-smooth muscle actin (alphaSMA), cadherins, and MMP-9. Because OTA nephrotoxicity is mediated by free radicals, we also investigated whether antioxidants in red wine provided protection for the kidney and attenuated OTA-induced EMT. Collagen content, determined by computerized analysis of Sirius red-stained kidney sections, increased in OTA, OTA-wine, and OTA-EtOH treated rats. In kidney cortex homogenates, COL-I and COL-III mRNA levels tended to rise in OTA treated rats, but were similar to CT after OTA-wine and OTA-EtOH administration. TIMP-1 gene expression was up-regulated in OTA, OTA-wine, and OTA-EtOH treated rats. LH2b mRNA/COL-I mRNA was significantly up-regulated in OTA-wine and OTA-EtOH treated rats, compared with CT and OTA alone. TGF-beta1 signaling tended to dominate after OTA, OTA-wine, and OTA-EtOH. MMP-1 protein levels were not affected. OTA induced proMMP-9 and alphaSMA overexpression, decreases of E-cadherin and N-cadherin, and DSC-2 up-regulation. OTA-wine caused a further, unexpected decrease of E- and N-cadherins and further up-regulation of OTA-induced DSC-2, while strongly reducing the OTA-induced increases of alphaSMA and proMMP-9. Posttranslational collagen modifications, such as decreased collagen degradation through MMP inhibition and increased collagen cross-links, seem to be key mechanisms leading to OTA-induced kidney cortex fibrosis. This mechanism was not affected by red wine in these conditions. Red wine seems to have some protective role against OTA-induced EMT, although without completely blocking the process and determining a condition in which abundant cells display an intermediate translational phenotype, but there are no alphaSMA or epithelial markers.

Effects of insulin-like growth factor-1 on cellular and molecular characteristics of bovine blastocysts produced in vitro

Addition of insulin-like growth factor-1 (IGF-1) to culture medium increases the proportion of bovine embryos that develop to the blastocyst stage and increases embryo survival following transfer to heat-stressed, lactating dairy cows. The objective of the present study was to determine molecular and cellular correlates of these actions of IGF-1. Embryos were produced in vitro and cultured for 7 days with or without 100 ng/ml IGF-1. On d 7 after insemination, grade 1 expanded blastocysts were harvested and used to determine total cell number, percent apoptosis, cell allocation to the inner cell mass and trophectoderm, and the relative abundance of several developmentally important gene transcripts. There was no significant effect of IGF-1 treatment on blastocyst cell number, the proportion of blastomeres that were apoptotic, or the number of cells in the inner cell mass and trophectoderm. However, differences in the relative abundance of several mRNA transcripts were observed between control and IGF-1 treated embryos. Addition of IGF-1 increased (P < 0.02) amounts of mRNA for IGF binding protein-3 and desmocollin II and tended (P < 0.08) to increase amounts of mRNA for Na/K ATPase and Bax. Moreover, IGF-1 treatment decreased (P < 0.05) steady-state amounts of transcripts for heat shock protein 70 and tended (P < 0.08) to reduce amounts of IGF-1 receptor mRNA. In conclusion, increased survival of embryos treated with IGF-1 does not appear due to effects on cell number, percent apoptosis, or cell allocation. Addition of IGF-1 to culture can, however, alter expression of several transcripts which may be important for embryo development and survival following transfer.

Tjp3/zo-3 is critical for epidermal barrier function in zebrafish embryos

TJP3/ZO-3 is a scaffolding protein that tethers tight junction integral membrane proteins to the actin cytoskeleton and links the conserved Crumbs polarity complex to tight junctions. The physiological function of TJP3/ZO-3 is not known and mice lacking TJP3/ZO-3 show no apparent phenotype. Here we show that Tjp3/Zo-3 is a component of tight junctions present in the enveloping cell layer of zebrafish embryos. Silencing tjp3/zo-3 using morpholinos leads to edema, loss of blood circulation and tail fin malformations in the embryos. The ultrastructure of tight junctions of the enveloping cell layer is disrupted, without affecting the asymmetric distribution of plasma membrane proteins. Morphants show a loss of the epidermal barrier, as assessed by an increased permeability of the enveloping cell layer to low molecular weight tracers and a higher sensitivity of the embryos to osmotic stress. Subjecting wild-type embryos to osmotic stress mimicks the morphant phenotype, consistent with the phenotype being a direct consequence of failed osmoregulation. Thus, Tjp3/Zo-3 is critical for barrier function of the enveloping cell layer and osmoregulation in early stages of zebrafish development.

Structure and function of desmosomes

Desmosomes are prominent adhesion sites that are tightly associated with the cytoplasmic intermediate filament cytoskeleton providing mechanical stability in epithelia and also in several nonepithelial tissues such as cardiac muscle and meninges. They are unique in terms of ultrastructural appearance and molecular composition with cell type-specific variations. The dynamic assembly properties of desmosomes are important prerequisites for the acquisition and maintenance of tissue homeostasis. Disturbance of this equilibrium therefore not only compromises mechanical resilience but also affects many other tissue functions as becomes evident in various experimental scenarios and multiple diseases.

Human embryos developing in vitro are susceptible to impaired epithelial junction biogenesis correlating with abnormal metabolic activity

BACKGROUND

Blastocyst biogenesis occurs over several cell cycles during the preimplantation period comprising the gradual expression and membrane assembly of junctional protein complexes which distinguish the outer epithelial trophectoderm (TE) cells from the inner cell mass (ICM). In the human, TE integrity and the formation of a junctional seal can often be impaired. Embryos likely to result in a successful pregnancy after transfer are mostly selected according to morphological criteria. Recent data suggest that non-invasive measurement of amino acid turnover may be useful to complement such morphological scores. Whether morphological and metabolic criteria can be linked to poor TE differentiation thereby underpinning developmental predictions mechanistically remains unknown.

METHODS

We examined TE intercellular junction formation in human embryos by immunofluorescence and confocal microscopy and correlated this process with morphological criteria and amino acid turnover during late cleavage.

RESULTS

Our results show that TE differentiation may be compromised by failure of membrane assembly of specific junction constituents. This abnormality relates more closely to metabolic profiles than morphological criteria.

CONCLUSION

Our data identify that amino acid turnover can predict TE differentiation. These findings are the first to link two mechanisms, metabolism and junction membrane assembly, which contribute to early embryo development.

Use of insulin-like growth factor-1 to improve post-transfer survival of bovine embryos produced in vitro

Use of in vitro produced embryos in commercial settings is limited by alterations in embryo function that result in reduced embryo and fetal survival and increased fetal, placental and neonatal abnormalities. One potential strategy to improve the efficiency of in vitro embryo production systems is to modify embryo culture conditions to more closely mimic embryo physiology in vivo. The milieu of the reproductive tract contains various growth factors and regulatory molecules which can regulate embryonic development. One of these molecules, insulin-like growth factor-1 (IGF-1), has been reported to have beneficial effects on bovine embryo development in vitro. Addition of IGF-1 to embryo culture can increase pregnancy and calving rates in lactating dairy cows. However, recent research indicates that such an effect is only observed when recipients are heat-stressed. In non-heat stressed animals, IGF-1 treatment does not affect conceptus length or interferon-tau secretion; thus, it is not likely that IGF-1 promotes embryo survival by blocking the luteolytic cascade. On the other hand, IGF-1 treatment can alter the relative abundance of certain developmentally important transcripts. Such differences may be important to improve embryo survival during heat stress. Further research into the effect of IGF-1 on gene expression and DNA methylation are warranted. Results indicate that modification of embryo culture with a growth factor can affect embryo survival after transfer. It is important that future research evaluating modifications to embryo culture also includes experiments involving transfer of embryos to recipients. Such experiments are important to demonstrate that proposed modifications actually improve post-transfer embryonic survival.

Relative contribution of cell contact pattern, specific PKC isoforms and gap junctional communication in tight junction assembly in the mouse early embryo

In mouse early development, cell contact patterns regulate the spatial organization and segregation of inner cell mass (ICM) and trophectoderm epithelium (TE) during blastocyst morphogenesis. Progressive membrane assembly of tight junctional (TJ) proteins in the differentiating TE during cleavage is upregulated by cell contact asymmetry (outside position) and suppressed within the ICM by cell contact symmetry (inside position). This is reversible, and immunosurgical isolation of the ICM induces upregulation of TJ assembly in a sequence that broadly mimics that occurring during blastocyst formation. The mechanism relating cell contact pattern and TJ assembly was investigated in the ICM model with respect to PKC-mediated signaling and gap junctional communication. Our results indicate that complete cell contact asymmetry is required for TJ biogenesis and acts upstream of PKC-mediated signaling. Specific inhibition of two PKC isoforms, PKCdelta and zeta, revealed that both PKC activities are required for membrane assembly of ZO-2 TJ protein, while only PKCzeta activity is involved in regulating ZO-1alpha+ membrane assembly, suggesting different mechanisms for individual TJ proteins. Gap junctional communication had no apparent influence on either TJ formation or PKC signaling but was itself affected by changes of cell contact patterns. Our data suggest that the dynamics of cell contact patterns coordinate the spatial organization of TJ formation via specific PKC signaling pathways during blastocyst biogenesis.

PKC signalling regulates tight junction membrane assembly in the pre-implantation mouse embryo

Epithelial differentiation including tight junction (TJ) formation occurs exclusively within the trophectoderm (TE) lineage of the mouse blastocyst. Here we examine mechanisms by which TJ protein membrane assembly might be regulated by protein kinase C (PKC) in the embryo. To overcome the inherent staging asynchrony of individual blastomeres within intact embryos, we have used isolated inner cell masses (ICMs) from early blastocysts to induce epithelial differentiation in their outer cells responding to their new cell contact pattern. Two TJ proteins examined retain their order of membrane assembly in isolated ICMs in culture as during normal development (early-assembling ZO-2 and late-assembling ZO-1α+), but this process is highly accelerated. Using six chemical modulators of PKC activity, we show here that PKC signalling is involved in the regulation of TJ membrane assembly. While indolactam-mediated PKC activation stimulates membrane assembly of both TJ proteins, TPA-mediated PKC activation stimulates only that of ZO-1α+. The PKC inhibitors Ro-31-8220, Ro-31-8425 and Gö 6983 suppress the stimulatory effect of both PKC activators on membrane assembly to varying extents according to inhibitor and TJ protein examined. Gö 6983 similarly inhibits ZO-2 and ZO-1α+membrane assembly. PKC inhibition by Gö 6976 appeared to stimulate TJ membrane assembly. Despite the broad PKC isotype specificity of the inhibitors used, these data suggest that the two TJ proteins are differently regulated by PKC isotypes or subfamilies. As Gö 6983 uniquely affects aPKC (particularly PKCζ) and we find that both PKCδ and ζ relocate upon activator treatment to colocalise partially with the TJ proteins in isolated ICMs, we suggest that at least PKCδ and ζ may play a central role in regulating TJ membrane assembly.

Timing of blastocyst expansion affects spatial messenger RNA expression patterns of genes in bovine blastocysts produced in vitro

Blastocyst formation and expansion are dependent on the differentiation and function of a proper transport of nutrients through the trophectoderm (TE) enclosing the inner cell mass (ICM). Coincident with compaction and cavitation, glucose becomes the preferred energy substrate of the early embryo. These hallmarks in early development require well-orchestrated gene expression patterns specifically with regard to timing and localization. The present study investigated the relative abundance (RA) of gene transcripts in the two lineages of in vitro-produced expanded bovine blastocysts in relation to timing of development, i.e., blastocyst expansion and localization of specific mRNAs. Expanded blastocysts from either Day 7 or Day 8 or isolated ICMs derived thereof were analyzed with the aid of a semiquantitative reverse transcriptase-polymerase chain reaction assay for gene transcripts, which are thought to play a pivotal role in blastocyst expansion, i.e., Na/K-ATPase alpha1 subunit (Na/K), E-cadherin (E-cad), zonula occludens protein-1 (ZO-1), desmocollin II (Dc II), plakophilin (Plako), trophoblastic function (interferon tau [IFtau]), and glucose transport (glucose transporter-1, -3, -4 [Glut-1, -3, -4]). Total cell number, ICM cell number, or ICM/total cells ratio were similar in Day 7 and Day 8 expanded blastocysts. Significant differences were determined in the RA for Na/K, E-cad, Dc II, Plako, and ZO-1 transcripts between TE cells of expanded blastocysts derived from either Day 7 or Day 8. The RA of Dc II, Glut-1, and Glut-4 was significantly decreased in the ICM compared with the TE at Day 7. Similarly, the RA of Na/K, Dc II, Glut-1, and Glut-4 at Day 8 of development was significantly decreased in the ICM compared with the TE. Interestingly, no differences were observed when comparing ICMs originating from blastocysts expanded at either Day 7 or Day 8. Plako and IFtau transcripts were not detected in isolated ICMs, indicating that expression of these mRNAs is restricted to the TE. In contrast, similar expression patterns within the ICM and TE were determined for Na/K, E-cad, ZO-1, and Glut-3 mRNA. Dc II, Glut-1, and Glut-4 were more abundant in the TE than in ICM. Results show that expression of developmentally important genes is related to the two cell lineages in the early embryo and emphasize the critical role of a well controlled spatial gene expression pattern for regular preimplantation development.

Expression of Wnt genes during mouse preimplantation development

Pattern formation in the mouse preimplantation embryo is tightly regulated and essential for successful development. Wnt genes are known to regulate cell interactions and cell fate in invertebrates and vertebrates and, therefore, may play a role in the specification of cell lineages and cellular interactions that occur in preimplantation development. Using degenerate primers based on conserved protein sequences in Wnt coding regions, we have found evidence for Wnt gene expression at the blastocyst stage of mouse preimplantation development. We have identified sequences encoding Wnts3a and 4 and confirmed that these are present as transcripts in early development by using reverse transcriptase-polymerase chain reaction (RT-PCR) with specific primers located in the 5' half of these Wnt genes. Studies on the timing of expression showed that Wnt3a transcripts were present in 2-cell embryos which may represent maternally or embryonically derived transcripts since the major transition of maternal to zygotic gene expression occurs during the late 2-cell stage. Both Wnt3a and 4 transcripts were detected in some precompact 4/8-cell stages with consistent expression detected in all compact 8-, 16-cell and blastocyst stages. To our knowledge, expression of Wnt genes has not been previously described at such an early stage of mammalian development.

Differential pattern of Xist RNA accumulation in single blastomeres isolated from 8-cell stage mouse embryos following laser zona drilling

Xist gene expression begins at the late 2-cell stage in female mouse embryos and by the third division results in the accumulation of an average 100 copies of Xist RNA per cell, as measured by real-time reverse transcription-polymerase chain reaction (RT-PCR). In the blastocyst, the trophectoderm maintains the paternally imprinted pattern of Xist expression present during early development, while either the maternal or the paternal X chromosome can express Xist among cells of the inner mass. Fluorescent in situ hybridization (FISH) has previously established that Xist transcripts are localized on the silenced X chromosome, forming aggregates of variable dimensions in blastomeres of 8-cell embryos. This observation and the fact that Xist RNA accumulation per cell sharply decreases after morula stage raise the possibility that cells of cleaving embryos contain different levels of Xist RNA, perhaps linked to their subsequent developmental fates. We show here that Xist RNA is efficiently recovered from single blastomeres isolated from 8-cell embryos following laser zona drilling. Sexing of the samples and simultaneous quantification of Xist RNA in individual cells is achieved with a multiplex Xist/Sry real-time RT-PCR assay sensitive to the single-copy level. This analysis reveals that Xist RNA is indeed accumulated to substantially different levels in individual blastomeres of the same 8-cell embryo and that two blastomeres contain most of the molecules per embryo. These results support the conclusion that cells of the early mammalian embryo are not all functionally equivalent. Differential Xist gene expression could arise from differences in DNA methylation, or the order in which cells divide.

Loss of desmoglein 2 suggests essential functions for early embryonic development and proliferation of embryonal stem cells

Desmoglein 2 (Dsg2) is a Ca(2+)-dependent adhesion molecule of desmosomes and is synthesized in all desmosome-bearing tissues from their earliest appearance onward. To examine the function of Dsg2, its gene was inactivated by homologous recombination in embryonal stem (ES) cells for the generation of knockout mice. DSG2 -/- mice and a considerable number of DSG2 +/- mice died at or shortly after implantation. On the other hand, DSG2 -/- blastocysts developed an apparently normal trophectoderm layer, the first tissue known to produce desmosomes, and hatched properly. Immunofluorescence analyses of these blastocysts showed, however, that the distribution of the desmosomal plaque protein desmoplakin was disturbed, whereas the adherens junction proteins E-cadherin and beta-catenin appeared to be unaffected. Unexpectedly, we found that Dsg2 seems to be essential for the inner cell mass and the ES cell population derived there from. We present evidence that Dsg2, which is located in desmoplakin-negative wild-type ES cells in non-desmosomal junctions, is needed for normal ES cell proliferation. Our observations thus reveal that important Dsg2 functions are desmosome-independent during early development and are needed for ES cell and early embryo survival.

The regulatory region of the human desmocollin 3 promoter forms a DNA four-way junction

Adhesion between desmosomal junctions is mediated by structural proteins of the cadherin family, viz. three desmocollins (DSC) and three desmogleins (DSG). Promoter and primer extension analysis of human DSC3 showed a TATA-less sequence initiating transcription via a cluster of sites upstream of the coding region. Deletion analysis of 1 kb of the promoter showed that expression is regulated between --303 and --203 bp upstream of the start-site of translation. Tertiary structure analysis of this cis-active region (cis 1) revealed a potential DNA 4-way junction which is notably G/C-rich in sequence. PAGE analysis of this region identified four differently migrating forms of the DNA. Structure-specific cleavage of the DNA with bacteriophage T7 endonuclease I showed the slowest migrating form to be either an extended/cruciform or stacked-X 4-way junction. DNA-binding, gel retardation assays of the cis 1 region showed distinct DNA-protein complexes and by competition experiments and using purified junction DNA we show that one of these complexes bound with both sequence and structure specificity to the 4-way junction DNA.

Cloning and expression throughout mouse development of mfat1, a homologue of the Drosophila tumour suppressor gene fat

We present the entire sequence of the mouse Fat orthologue (mFat1), a protein of 4,588 amino acids with 34 cadherin repeats, 27 potential N-glycosylation sites, five EGF repeats and a laminin A G-motif in its extracellular domain. A single transmembrane region is followed by a cytoplasmic domain containing putative catenin-binding sequences. mFat1 shows high homology to human FAT and lesser homology to Drosophila Fat. The sequence of this giant cadherin suggests that it is unlikely to have a homophilic adhesive function, but may mediate heterophilic adhesion or play a signalling role. Expression analysis shows that the mfat1 gene is expressed early in pre-implantation mouse development, at the compact eight cell stage. Whole-mount and section in situ analyses show that transcripts are widely expressed throughout post-implantation development, most notably in the limb buds, branchial arches, forming somites, and in particular in the proliferating ventricular zones in the brain, being down-regulated as cells cease dividing. RT-PCR detects widespread expression in the adult suggesting a role in proliferation and differentiation of many tissues and cell types.

Post-translational control of occludin membrane assembly in mouse trophectoderm: a mechanism to regulate timing of tight junction biogenesis and blastocyst formation

The mouse blastocyst forms during the 32-cell stage with the emergence of the blastocoelic cavity. This developmental transition is dependent upon the differentiation and transport function of the trophectoderm epithelium which forms the wall of the blastocyst and exhibits functional intercellular tight junctions (TJs) to maintain epithelial integrity during blastocoele expansion. To investigate mechanisms regulating the timing of blastocyst formation, we have examined the dynamics of expression of occludin, an integral membrane protein of the TJ. Confocal microscopy of intact embryos and synchronised cell clusters revealed that occludin first assembles at the apicolateral membrane contact site between nascent trophectoderm cells usually during the early 32-cell stage, just prior to the time of blastocoele cavitation. This is a late event in the assembly of TJ-associated proteins within trophectoderm which, from our previous data, spans from 8- to 32-cell stages. Occludin membrane assembly is dependent upon prior E-cadherin-mediated cell-cell adhesion and is sensitive to brefeldin A, an inhibitor of Golgi-to-membrane transport. Occludin is delivered to the TJ site in association with the TJ plaque protein, ZO-1(α)+, which we have shown previously is newly transcribed and translated during late cleavage. Immediately after assembly and before cavitation, occludin localised at the TJ site switches from a Triton X-100-soluble to -insoluble form indicative of actin cytoskeletal and/or membrane anchorage. Occludin mRNA and protein are detectable throughout cleavage by RT-PCR and immunoblotting, respectively, indicating that timing of membrane assembly is not controlled by expression alone. Rather, we have identified changes in the pattern of different occludin forms expressed during cleavage which, using phosphatase treatment of embryo lysates, include post-translational modifications. We propose that the phosphorylation of one form of occludin (band 2, 65–67 kDa) during late cleavage, which leads to its exclusive conversion from a Triton X-100-soluble to -insoluble pool, may regulate occludin association with ZO-1(α)+ and membrane assembly, and thereby act to control completion of TJ biogenesis and the timing of blastocyst formation.

Clustered cadherin genes: a sequence-ready contig for the desmosomal cadherin locus on human chromosome 18

We describe the assembly of a cosmid and PAC contig of approximately 700 kb on human chromosome 18q12 spanning the DSC and DSG genes coding for the desmocollins and desmogleins. These are members of the cadherin superfamily of calcium-dependent cell adhesion proteins present in the desmosome type of cell junction found especially in epithelial cells. They provide the strong cell-cell adhesion generated by this type of cell junction for which expression of both a desmocollin and a desmoglein is required. In the autoimmune skin diseases pemphigus foliaceous and pemphigus vulgaris (PV), where the autoantigens are, respectively, encoded by the DSG1 and DSG3 genes, severe areas of acantholysis (cell separation), potentially life-threatening in the case of PV, are evident. Dominant mutations in the DSG1 gene causing striate palmoplantar keratoderma result in hyperkeratosis of the skin on the parts of the body where pressure and abrasion are greatest, viz., on the palms and soles. These genes are also candidate tumor suppressor genes in squamous cell carcinomas and other epithelial cancers. We have screened two chromosome 18-specific cosmid libraries by hybridization with previously isolated YAC clones and DSC and DSG cDNAs, and a whole genome PAC library, both by hybridization with the YACs and by screening by PCR using cDNA sequences and YAC end sequence. The contigs were extended by further PCR screens using STSs generated by vectorette walking from the ends of the cosmids and PACs, together with sequence from PAC ends. Despite screening of two libraries, the cosmid contig still had four gaps. The PAC contig filled these gaps and in fact covered the whole locus. The positions of 45 STSs covering the whole of this region are presented. The desmocollin and desmoglein genes, which are about 30-35 kb in size, are quite well separated at approximately 20-30 kb apart and are arranged in two clusters, one DSC cluster and one DSG cluster, which are transcribed outward from the interlocus region. The order of the genes is correlated with the spatial order of gene expression in the developing mouse embryo, and this, and previous transgenic experiments, suggests that long-range genetic elements that coordinate expression of these genes may be present. The complete bacterial clone contig described in this paper is thus a resource not only for future sequencing but also for investigations into the control of expression of these clustered genes.

Alterations in the relative abundance of gene transcripts in preimplantation bovine embryos cultured in medium supplemented with either serum or PVA

In preimplantation bovine embryos, the relative abundance of various developmentally important gene transcripts was determined by a semi-quantitative RT-PCR assay to analyze the effects of two medium supplements, serum or polyvinyl alcohol (PVA). Development to morula, blastocyst, and hatched blastocyst stages was higher (P < or = 0.05) in medium supplemented with serum than in medium supplemented with PVA. Connexin43 mRNA expression virtually disappeared from the 8-16 cell stage onward, but reappeared in the hatched blastocyst in serum-supplemented medium, whereas it was detected in PVA-derived embryos throughout development. No differences were found for plakophilin mRNA between both culture groups. Desmocollin II mRNA showed a sharp increase at the blastocyst stage in both groups with a higher transcription level in PVA-generated embryos. A significant difference in desmocollin III transcripts was detectable at the 8-16-cell stage between serum- and PVA-derived embryos. Transcripts for desmoglein 1 and desmocollin I were not detected at any preimplantation stage, irrespective of medium supplementation. The relative abundance of glucose-transporter-1 mRNA was significantly increased at the 8-16-cell stage in embryos produced in medium supplemented with PVA, but not serum. Heat shock protein and poly(A)polymerase mRNA were continuously expressed during preimplantation development in both culture groups. Although poly(A)polymerase mRNA was significantly elevated in PVA- over serum-derived embryos, heat shock protein mRNA expression was significantly enhanced in serum-generated embryos over PVA-derived embryos. Interferon tau mRNA showed a significant increase at the hatched blastocyst stage only in PVA-supplemented medium. These data suggest that alterations in mRNA expression are associated with culture environment. Timing and magnitude of the alterations varied among the different transcripts and were significantly affected by the presence of exogenous protein in a stage-specific manner, predominantly at critical developmental time points.

Desmoplakin is required early in development for assembly of desmosomes and cytoskeletal linkage

Desmosomes first assemble in the E3.5 mouse trophectoderm, concomitant with establishment of epithelial polarity and appearance of a blastocoel cavity. Throughout development, they increase in size and number and are especially abundant in epidermis and heart muscle. Desmosomes mediate cell-cell adhesion through desmosomal cadherins, which differ from classical cadherins in their attachments to intermediate filaments (IFs), rather than actin filaments. Of the proteins implicated in making this IF connection, only desmoplakin (DP) is both exclusive to and ubiquitous among desmosomes. To explore its function and importance to tissue integrity, we ablated the desmoplakin gene. Homozygous -/- mutant embryos proceeded through implantation, but did not survive beyond E6.5. Surprisingly, analysis of these embryos revealed a critical role for desmoplakin not only in anchoring IFs to desmosomes, but also in desmosome assembly and/or stabilization. This finding not only unveiled a new function for desmoplakin, but also provided the first opportunity to explore desmosome function during embryogenesis. While a blastocoel cavity formed and epithelial cell polarity was at least partially established in the DP (-/-) embryos, the paucity of desmosomal cell-cell junctions severely affected the modeling of tissue architecture and shaping of the early embryo.

Desmosomes: intercellular adhesive junctions specialized for attachment of intermediate filaments

Cell-cell adhesion is thought to play important roles in development, in tissue morphogenesis, and in the regulation of cell migration and proliferation. Desmosomes are adhesive intercellular junctions that anchor the intermediate filament network to the plasma membrane. By functioning both as an adhesive complex and as a cell-surface attachment site for intermediate filaments, desmosomes integrate the intermediate filament cytoskeleton between cells and play an important role in maintaining tissue integrity. Recent observations indicate that tissue integrity is severely compromised in autoimmune and genetic diseases in which the function of desmosomal molecules is impaired. In addition, the structure and function of many of the desmosomal molecules have been determined, and a number of the molecular interactions between desmosomal proteins have now been elucidated. Finally, the molecular constituents of desmosomes and other adhesive complexes are now known to function not only in cell adhesion, but also in the transduction of intracellular signals that regulate cell behavior.

Antisense expression of a desmocollin gene in MDCK cells alters desmosome plaque assembly but does not affect desmoglein expression

The desmocollins are one of two types of putative adhesive proteins present in the desmosome type of cell junctions, the other type being the desmogleins; both are members of the cadherin superfamily. Each type of desmosomal cadherin occurs as a number of isoforms which have differing tissue distribution; within stratifying epithelia some isoforms occur only suprabasally. We have sought to analyse desmocollin function by reducing the amount of protein using antisense gene expression in the widely studied Madin-Darby canine kidney (MDCK) cell line. Although this is a simple epithelial cell line, we show by Northern blot analysis that it expresses multiple isoforms of the desmosomal cadherins. Desmocollins DSC2 and DSC3 and desmogleins DSG2 and DSG3 (the pemphigus vulgaris antigen PVA) were detected, but DSC1 and DSG1, which are present exclusively in the suprabasal layers of the epidermis, were absent. The major desmocollin isoform was the type 2 (DSC2). A DSC2 clone isolated from a MDCK cDNA library had the same cell adhesion recognition sequence (Phe-Ala-Thr) as human, bovine and mouse type 2 isoforms. This sequence appears diagnostic for the three desmocollin isoforms. This cDNA clone was used to isolate a genomic DSC2 clone; antisense expression of this clone in MDCK cells resulted in a drastic reduction of desmocollin protein as judged by Western blots; Dsc3 was not upregulated to compensate for the loss of Dsc2. This antisense expression significantly altered desmosome assembly. There was a loss of punctate staining evident when using a desmosome plaque protein (desmoplakin) antibody. Electron microscopy revealed that there was a reduction in the number of desmosomes and a notable increase in the asymmetry of plaques between adjacent cells. Immunolabelling showed that similar levels of desmogleins and E-cadherin were present. Immunoelectron microscopy also showed that many vesicular structures were labelled, at intervals along the lateral membranes between cells. The distinctive loose organization of the remaining desmosomes may originate in modifications to the targeting and incorporation of proteins into fully assembled plaques. Other junctions were unaffected and the cells maintained their integrity as a confluent monolayer.

Analysis of variation in relative mRNA abundance for specific gene transcripts in single bovine oocytes and early embryos

Variation in the abundance of a specific gene transcript was assessed in single bovine oocytes and in vitro-derived blastocysts. Transcripts encoding the Na+,K(+)-ATPase alpha 1 subunit were detected by reverse-transcription polymerase chain reaction (RT-PCR) and quantified relative to an exogenously supplied rabbit alpha-globin mRNA using laser-induced fluorescence capillary electrophoresis (LIF-CE). The precision of this relative abundance (RA) calculation was predicted and shown to resolve 2-fold differences in transcript abundance between individual blastocysts and predicted in oocytes to resolve 3-fold differences. The RA of the alpha 1 subunit transcript differed by 2- to 3-fold among blastocysts, and 3- to 6-fold among oocytes. Comparison of a general population of oocytes with blastocysts revealed little overlap in RA values between the two groups, with a 8- to 14-fold increase in the mean RA for each group with development observed in two successive experiments (P < or = 0.05). In contrast, oocytes selected for their developmental competence on the basis of morphologic criteria exhibited only a 1.6- to 1.7-fold developmental increase when the assay was performed on cDNA generated from either embryo pools (n = 6 versus 6) or individuals (n = 7 versus 7), respectively. These results provide the first characterization of the degree of heterogeneity in the abundance of a specific mRNA transcript among individual mammalian oocytes and preimplantation embryos and demonstrate that transcript relative abundance can be correlated with bovine oocyte morphology.

Changing pattern of desmocollin 3 expression accompanies epidermal organisation during skin development

The adhesive core of the desmosome is composed of cadherin-like glycoproteins of 2 families, desmocollins and desmogleins. The desmosomal cadherins show distinct patterns of expression in adult epidermis, and we have suggested that the desmocollins have a functional role in regulating the differentiation and/or morphogenesis of that epithelium (North et al. [1996] Proc. Natl. Acad. Sci. USA 93:7701-7705.). To examine this hypothesis, we cloned murine desmocollins and examined the induction patterns of desmocollins 1 and 3 during skin and skin appendage development. Desmocollins 3 and 1 were first expressed in epidermis in highly regional patterns at embryonic days 13.0 and 13.5, respectively, and both were up-regulated in general body epidermis at day 14.5. At this stage, epidermis is undifferentiated and the desmocollins showed an unexpected expression pattern. However, by day 18.5 when skin had undergone terminal differentiation, desmocollin 1 and 3 expression resembled that found in the adult. Thus, the establishment of the adult pattern of desmocollin expression corresponds to the adult pattern of epidermal stratification. We suggest that it is the ratio of desmocollin 1 to desmocollin 3 expression at different levels in the epidermis that is fundamental in establishing this pattern of differentiation.

A YAC contig joining the desmocollin and desmoglein loci on human chromosome 18 and ordering of the desmocollin genes

The desmocollins and desmogleins are members of the cadherin family of adhesive proteins present in the desmosome type of cell-cell junction. All of the known desmoglein and desmocollin isoforms, which have differing tissue and developmental distributions, are coded by very closely linked genes at 18q12.1. We have previously described YAC clones carrying all three known desmoglein (DSG) genes. We have now isolated YAC clones that carry all three known desmocollin genes (DSC1, 2, and 3) from two libraries and also isolated clones that join the DSC locus to the DSG locus, forming a complete contig for the region. Absence of chimeric ends for some of the YACs was confirmed by isolating Vectorette PCR products for the YAC ends and mapping the derived DNA sequences back to other YACs from CEPH. The whole DSC/DSG gene complex occupies no more than about 700 kb, and the genes are arranged in the order cen-3'-DSC3-DSC2-DSC1-5'-5'-DSG1-DSG3-D SG2-3'-tel, so that the two gene clusters are transcribed outward from the interlocus region. A P1 clone carrying part of DSC2 and DSC3 confirmed the relative orientation of transcription of these two genes. The conservation of close genetic linkage may be of trivial importance related to the recent duplication of these genes or may be because there is a region within the locus that is involved in coordinating the expression of the desmoglein and desmocollin genes.

Tight junction assembly during mouse blastocyst formation is regulated by late expression of ZO-1 alpha+ isoform

The mouse preimplantation embryo has been used to investigate the de novo synthesis of tight junctions during trophectoderm epithelial differentiation. We have shown previously that individual components of the tight junction assemble in a temporal sequence, with membrane assembly of the cytoplasmic plaque protein ZO-1 occurring 12 hours before that of cingulin. Subsequently, two alternatively spliced isoforms of ZO-1 (alpha+ and alpha-), differing in the presence or absence of an 80 residue alpha domain were reported. Here, the temporal and spatial expression of these ZO-1 isoforms has been investigated at different stages of preimplantation development. ZO-1alpha- mRNA was present in oocytes and all preimplantation stages, whilst ZO-1alpha+ transcripts were first detected in embryos at the morula stage, close to the time of blastocoele formation. mRNAs for both isoforms were detected in trophectoderm and ICM cells. Immunoprecipitation of 35S-labelled embryos also showed synthesis of ZO-1alpha- throughout cleavage, whereas synthesis of ZO-1alpha+ was only apparent from the blastocyst stage. In addition, 33P-labelling showed both isoforms to be phosphorylated at the early blastocyst stage. The pattern and timing of membrane assembly of the two isoforms was also distinct. ZO-1alpha- was initially seen as punctate sites at the cell-cell contacts of compact 8-cell embryos. These sites then coalesced laterally along the membrane until they completely surrounded each cell with a zonular belt by the late morula stage. ZO-1alpha+ however, was first seen as perinuclear foci in late morulae before assembling at the tight junction. Membrane assembly of ZO-1alpha+ first occurred during the 32-cell stage and was zonular just prior to the early blastocyst stage. Immunostaining indicative of both isoforms was restricted to the trophectoderm lineage. Membrane assembly of ZO-1alpha+ and blastocoele formation were sensitive to brefeldin A, an inhibitor of intracellular trafficking beyond the Golgi complex. In addition, the tight junction transmembrane protein occludin co-localised with ZO-1alpha+ at the perinuclear sites in late morulae and at the newly assembled cell junctions. These results provide direct evidence from a native epithelium that ZO-1 isoforms perform distinct roles in tight junction assembly. Moreover, the late expression of ZO-1alpha+ and its apparent intracellular interaction with occludin may act as a final rate-limiting step in the synthesis of the tight junction, thereby regulating the time of junction sealing and blastocoele formation in the early embryo.

Cloning and transcriptional analysis of the promoter of the human type 2 desmocollin gene (DSC2)

The desmocollins, together with the desmogleins, are members of the cadherin family and constitute the adhesive proteins of the desmosome type of cell-cell junction. Here we describe a study of the promoter of the human form of the DSC2 gene which is the equivalent of the first isoform expressed in the developing mouse embryo and that has the most widespread tissue distribution in epithelia and also in desmosome-bearing non-epithelial tissues. Analysis of the 5' upstream region by DNA sequencing and Southern blotting suggested that it contained a CpG island, and a major site of transcription initiation 201 bp upstream of the translation start site was found by RNase protection and primer extension. There were no obvious CCAAT or TATA boxes present. Analysis of 1.9 kb upstream of the translation start site revealed consensus binding sites for transcription factors including Ap-2 and Sp-1, and motifs common to the promoters of other epithelially expressed genes such as keratin 14 and the desmoglein genes DSG1 and DSG3. Deletion derivatives defined a promoter of 525 bp which was active in epithelial cells and in mouse blastocysts with an intact epithelium. This promoter showed reduced expression in non-epithelial cells.

Desmosomes: differentiation, development, dynamics and disease

Recent evidence on the distribution of desmosomal glycoprotein isoforms that shows their combined expression in individual desmosomes has strengthened the belief that the latter are involved in epithelial differentiation and morphogenesis. It has been shown that cellular interactions and protein kinase C can modulate the adhesive properties of desmosomes in epithelial cell sheets. Genetic studies indicate the involvement of desmosomal components in cancer and epidermal diseases.

Cadherin cell adhesion molecules in differentiation and embryogenesis

The cadherin gene superfamily of calcium-dependent cell-cell adhesion molecules contains more than 40 members. We summarize functions attributed to these proteins, especially their roles in cellular differentiation and embryogenesis. We also describe hierarchies of protein-protein interactions between cadherins and cadherin-associated proteins (catenins). Several signal transduction pathways converge on, and diverge from, the cadherin/catenin complex to regulate its function; we speculate on roles of these signaling processes for cell structure and function. This review provides a framework for interpretation of developmental functions of cadherin cell adhesion molecules.

The desmocollins of human foreskin epidermis: identification and chromosomal assignment of a third gene and expression patterns of the three isoforms

A third human desmocollin, designated DSC3, was identified in foreskin epidermis by reverse transcriptase-polymerase chain reaction (PCR) using degenerate desmocollin primers. cDNA clones covering the entire coding sequence of the longer DSC3 splice variant were isolated and sequenced. Sequence comparisons indicated that this new desmocollin showed greater homology (67% amino acid identity) with the original human desmocollin (now designated DSC2) than with DSC1 (52% amino acid identity) although it had a unique potential cell adhesion recognition site (YAS). DSC3 was assigned to chromosome 18 by PCR analysis of rodent-human somatic cell hybrids, where it appears to be closely linked to all the other desmosomal cadherin genes. The expression of the three human desmocollins was examined in foreskin epidermis by in situ hybridization with 3'-untranslated riboprobes and by immunofluorescence with isoform-specific anti-peptide antibodies. DSC1 was present in the upper spinous/granular layers but not in the basal/lower spinous layers of the tissue. DSC2 and DSC3 were present in most of the living layers of the epidermis. DSC1 was not detected in any of the nonkeratinizing human epithelia examined (buccal mucosa, cervix, esophagus), indicating that it is specific for the keratinizing epithelium of the epidermis. However, all these internal epithelia expressed DSC2 and DSC3, and both were present in most of the living layers of the tissues including the basal layers.

Epithelial differentiation in the mouse preimplantation embryo: making adhesive cell contacts for the first time

The preimplantation embryo generates two distinct tissues, the trophectoderm, which is a transporting polarized epithelium, and the inner cell mass. Epithelial differentiation and tissue segregation, here examined in relation to the maturation of membrane adhesion and cell junction systems, are coordinated events regulated by a combination of the zygotic gene expression programme, kinase-mediated protein activation and cell-cell interactions.